Alright , the idea is basically a pile of sand(amount undetermined) that move kind of like a swarm of insects. If you were to look at it, you'd see a large cloud of sand blazing toward you. The sand will "search" for other masses of sand, which if contact with normal sand is made, It too will become part of the SCP. When enough sand is gathered , The SCP will start to form massive Structures. Sand castles, if you will. Eventually forming cities of nothing but sand. If other structures stand in it's way, it will simply engulf the structure and swarm around at incredible speeds and wear it down to the point where nothing is left in its place. Been done? Hope not.